Tascam Tsr-8 troubleshooting

R

Ryan Murphy

New member
Hi all!...

So I made a mistake.... I have the above mentioned half inch reel to reel.... I replaced the up take reel spring because it was bent. So have the pub open; I am about to adjust the tension for the spring and mistakenly touch the pub with the screwdriver. The whole thing goes haywire. Now none of the buttons function. It turns on the motor kicks on but that is it. The red lights underneath are out every other. The red led for the even tracks I think... is the code for something... is the whole thing fried? Some way I can reset? Looks like I may need to start replacing pcbs...? Some advice would help. I eill get a picture up.
 
Ryan,

Welcome and so sorry for your plight. I have been exactly where you are. It was almost 8 years ago I wasn't careful and fried my pristine Tascam 58. To this day I nervously take care whenever working on equipment...checking myself once, twice, even three times to make sure I'm about to do the correct action and making sure proper safeguards are in place.

Unfortunately just based on what you are describing I suspect there is/are (a) damaged logic component(s). But before we jump to that have you checked all the fuses? That means removing each one and testing with an ohm meter, and additionally can you be more specific about what touched what? What PCB did the screwdriver touch and where? Be as specific as you can. Do you see any scorching or damage and to what components?
 
I checked all the fuses and they're good. Now I press the button, the reels jolt, but nothing else happens; no lights come on, and nothing functions. The close up is the general vicinity of where i tuouched with the screwdriver now visible marks... Maybe I crossed u29 or u28? static maybe? There was no spark.
 
We still can't see the pic.

You may need to have a certain number of posts before you can post a pic. Otherwise maybe try posting the pic again?

If the situation is degrading and the fuses are good I really do suspect there is component level damage. I'm really sorry to say. I know how this feels.

We need to know what PCB has the damaged components to advise any further, and the pic would help too. But to avoid any sugar-coating my opinion is you are likely going to need to take it to a local tech to resolve this. But we can see if we can accomplish something ahead of that...need more info first.
 
I think you have to post 5 times before you can post images. As for the TSR-8, this is not sounding good. This reminds me, I need to try and get some non-conductive tools for this kind of job.

What follows is an educated guess based on the schematics and your description. U28 and U29 on the control board are both Darlington arrays (M54517P) and yes, they are right next to the tension adjustment pots. Unfortunately some pins of U29 are connected directly to the CPU. Most of the other connections to U28 and U29 are linked to the CPU via buffers in the form of U17 (7400 quad NAND gate) U7 (7404 hex inverter) and U4 (7402 quad NOR gate), so if you're astonishingly lucky, you might be able to bring the system up by taking a shotgun approach and replacing those five chips. However, the fact that the system no longer appears to boot is not encouraging.

If the CPU itself has been toasted, you're effectively going to have to replace the entire control board since the CPU has a factory-programmed ROM and an off-the-shelf replacement won't.
 
Is there a way to figure out if the cpu is fried? In the past it was always turn it on see if it warms up.

It is the controls pcb that I was working on. Last night I observed a flash around the fuse area when I had the case off. That only happened once. I don't think it was a static discharge that caused this I most likely shorted something out as I had the machine on.
 
When you say, "effectively replace the entire board"; that dosn't mean replace all the components on the board, it means find a new one and drop it in? At this point I am wondering if the other boards got fried too.
 
DSC_0239-2.JPG I think I probably crossed the pins on u29 because I touched down some where North west of r102.

It seemed like though, from what I remember; that I just touched the board and no components.
 
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Ryan Murphy said:
When you say, "effectively replace the entire board"; that dosn't mean replace all the components on the board, it means find a new one and drop it in? At this point I am wondering if the other boards got fried too.
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Yes, if the CPU is dead you'll have to find a control board from a scrap TSR-8. It's possible the MSR-16 control board would work too, since the TSR-8 has vestigial features from that deck (e.g. the spooling mode logic with no button attached to it) but I wouldn't bank on that. Another TSR-8 control board would be your best bet if it comes to that.

Obviously if there is a way to fix the board by replacing dead components that would be vastly preferable but it would not be easy to figure out which ones are dead. And unfortunately the microcontrollers and CPU on this deck are custom parts which you can't buy off-the-shelf.

All the same, it might be worth starting to troubleshoot from the power supply onwards, since even a fully-working CPU is going to malfunction if the power is dirty or insufficient.


EDIT: Quick sanity check. In your photo most of the connectors have been unplugged. I presume that when you're testing the machine they have all been plugged in again (and in the RIGHT places)?
 
Jomorris rocks.

He means swap out the entire board.

Maybe you just touched the board, maybe not, but the proof is in the pudding. You touched *something* and now it's not working.

My gut says:

1. The entire board will probably need replaced
2. Other boards are not affected

But that's just my gut opinion.
 
Yes. I only had it unplugged for half hour tops. Left em all right next to there slot. I plugged it ba k in hoping it would help and thats when the lights stop working. Yes. I Emailed tascam hoping they might have a new board... They had springs...? So...
 
sweetbeats said:
Jomorris rocks.
Click to expand...

Thanks. From you, that's high praise indeed.

Ryan, best of luck with this. If you had been in the UK, I have a spare deck that I could stand to part with, but shipping it transatlantic is going to exceed the value of the machine. Whether or not you can get a replacement control board off TASCAM, it's a good idea to look for a beaten-up TSR-8 on ebay as a source of parts.

If it's any consolation I blew out the peak LED circuit on channel 13 of my Otari by doing exactly the same thing. You can get ceramic adjustment tools for this and I'm going to try and snag one.
 
jpmorris said:
Thanks. From you, that's high praise indeed.
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Well shucks. Really...I quickly get lost in anything logic-circuitry related and your knowledge in this area (and others) is a real benefit to this forum, jpmorris. :guitar:

All good advice here methinks, Ryan Murphy. Your best bet is probably going to be looking for a beat up TSR-8 on eBay as jpmorris suggested, but let us know what Tascam comes back with and otherwise keep us posted. Again, awful sorry for your plight. It sucks, but you do have some paths to pursue.
 
I suspect that the damage you did was not all that serious but that a local power supply is out. The IC that you touched is not a uprocessor but a cheap support chip or a HC type logic IC. There are tests you can do for processor chips but you have to have more knowledge than basic DC to work on these. I have worked on at least a dozen of these and I have never had any accidents like this and I am just as likely to touch the board as you. Shorting pins on U29 is no big deal and all it will require is a new IC of that type. Mouser probably has it. It is best to consult an experienced Technician rather than jump to far fetched conclusions and have doom and disaster where there is only a minor repair.

IC U29 is just a 7 package darlington transistor array capable of 400mA.
They have them here- IF that is the problem.
1PCS M54517P 7 UNIT 400MA DARLINGTON TRANSISTOR ARRAY DIP16 | eBay
 
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Board swapping is the last resort and of the people that I have helped with technical issues it only works 1 out of 10 times.
In service business we do not swap boards but fix what you have there. The different model board is NOT going to be the same and I have never known that to be true- it is the wrong path to go down and I think it will result in even further destruction. Just because two models have some same functions does not mean their processor programming is the same.
 
skywaveTDR said:
I suspect that the damage you did was not all that serious but that a local power supply is out. The IC that you touched is not a uprocessor but a cheap support chip or a HC type logic IC.
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That is correct, but misses the point that U29 sits between a 15V supply line and the CPU (U9), with absolutely no protection between the two. Depending on exactly which pins are shorted it is very possible to send +15V into the I/O pins of a fragile CMOS processor which is expecting +7V as an absolute maximum. Personally, if the damage was simply the Darlington arrays themselves, I would have expected the boot sequence to complete but the tape tension to be shot when the transport is engaged.

Again, it would be wise to verify that the PSU is outputting correct voltage to the logic board before doing anything drastic, and as has previously been mentioned, I hope that it's something minor but it is unfortunately quite easy to cook a microcontroller by shorting the wrong pins on it.
 
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